A holographic stereogram is prepared as follows. For example, an object is sequentially picked up from different observation view points, to obtain a number of images. These images which are used as original images are recorded sequentially as hologram elements in form of strips or dots onto a piece of hologram recording medium, by means of an image recording apparatus.
For example, as shown in FIG. 1, a holographic stereogram having parallax information in only the lateral direction is prepared in a manner in which a plurality of original images 101a to 101e obtained by sequentially picking up an object 100 from different observation points in the lateral direction are sequentially recorded as strip-like hologram elements 102 onto a hologram recording medium by an image recording apparatus. A plurality of original images which are recorded as hologram elements onto the hologram recording medium are not always limited to those images that are obtained by actually picking up the object 100 but may be CAD (Computer Aided Design) images or CG (Computer Graphics) images.
In case of this holographic stereogram, pieces of image information obtained by sequentially picking up an object from different observation points in the lateral direction are sequentially recorded as strip-like hologram elements in the lateral direction. Therefore, when this holographic stereogram is observed with eyes by an operator, two-dimensional images respectively projected on the left and right eyes are slightly different from each other. As a result, the operator feels parallax and understands these images as a three-dimensional image.
Meanwhile, an image recording apparatus records hologram elements of a holographic stereogram onto a hologram recording medium using a photosensitive material as a recording material, in the following manner. That is, in case of preparing a holographic stereogram of a reflection type, a laser beam having a good interference characteristic is branched into two beams, and one of the two beams is irradiated, as a projection image (object light) subjected to two-dimensional image modulation by an image display means such as a liquid crystal panel or the like, onto one surface of a hologram recording medium. Also, in the image recording apparatus, the other one of the two branched laser beams is irradiated, as reference light, onto the other surface of the hologram recording medium. As a result, an interference fringe is formed, as a change of the refraction factor or a change of the transmittance, in the photosensitive material ofthe hologram recording medium, and thus, ahologram element is recorded.
For the image recording apparatus for recording hologram elements of a holographic stereogram onto a hologram recording medium, it is necessary to fix perfectly the hologram recording medium during exposure of a recording image so that even a slight vibration which is as small as the order of wavelength of light might not be generated, in orderto prepare aholographic stereogram which provides an excellent reproduced image.
The image recording apparatus is arranged so as to record sequentially a large number ofhologram elements while transferring the hologram recording medium little by little. Therefore, in case where a hologram recording medium is transferred, for example, with use of an electrically movable stage, a vibration is caused in the hologram recording medium itself as the medium is transferred. Accordingly, in this kind of image recording apparatus, exposure must be carried out after a vibration caused by transfer of a hologram recording medium is attenuated, in order to prepare a holographic stereogram which provides an excellent reproduced image. Therefore, there is a problem that a very long time is required to prepare one holographic stereogram and the productivity is low.
The present invention hence has an object of providing an image recording apparatus by which vibrations of a hologram recording medium are reduced and a holographic stereogram which provides an excellent reproduced image can be prepared in a short time period.